The present invention relates to a hydro dynamic gas bearing and a disk drive using the bearing.
In recent years, there is a tendency to increase speed and storage capacity of a recording/reproducing disc drive such as a magnetic disk, and particularly, achieving high-density recording is essential in increasing the storage capacity. To this end, highly accurate rotation technique of a main rotary shaft is required, and there is a move afoot to adopt a highly accurate hydro dynamic gas bearing in place of a conventional ball bearing or a cylindrical slide bearing.
FIGS. 4 and 5 show disk drives using a conventional hydro dynamic gas bearing.
In FIG. 4, a plurality of zigzag-shaped hydro dynamic pressure grooves 8 are formed on an outer peripheral surface of a shaft 9 to generate a hydro dynamic pressure subject to loads in radial and thrust directions. The shaft 9 is secured to a base 7 and inserted into a sleeve 10 so as to rotatably support the sleeve 10.
A circular coil 6 is provided on the base 7 by being inserted into a recess 10A formed in the sleeve 10. On an inner wall of the recess 10A, an annular magnet 5 is provided opposite the coil 6. Mounted to the sleeve 10 is a disk 14 which can magnetically or optically record/reproduce signals.
The bearing shown in FIG. 4 is accommodated in an inner space 13a defined by a casing 13 and the base 7 as shown in FIG. 5.
At the time of feeding a current through the coil 6, an electromagnetic force is generated between the magnet 5 and the coil 6 to rotate the sleeve 10 in a direction of arrow B. By this rotation, under a pumping action of the hydro dynamic pressure generating grooves 8 formed on the shaft 9, an air pressure in a sleeve inner space 11 between the shaft 9 and the sleeve 10 is locally increased to be higher than an outside air pressure. By the increased air pressure, the sleeve 10 is supported in a radial direction (direction of arrow R) of the shaft 9.
The hydro dynamic pressure generating grooves 8 are formed in an asymmetrical pattern with respect to radial-directional lines passing vertexes of each zigzag pattern. The pumping action thus caused generates an airflow which flows from a bottom to a top in the sleeve inner space 11 to increase an air pressure in a space 11A at a top of the shaft 9 to be higher than the outside air pressure. As a result, the sleeve 10 moves upward with respect to the shaft 9 in an axial direction (thrust direction) of the shaft.
A vent plate 1 of a cap 3 provided above the sleeve 10 has an air vent 2, so that the high-pressure air in the space 11A is discharged outward through the air vent 2. Setting a diameter of the air vent 2 to a predetermined value allows the air pressure to be kept at a constant value and allows an amount of upward movement of the sleeve 10 in the thrust direction to be kept at a predetermined value. In this way, the sleeve 10 is rotated in a contactless fashion with the shaft 9.
And, recording signals on the disk 14 or reading signals from the disk 14 is performed by means of a head 16 mounted to a head arm 17 which is driven to oscillate around an oscillation shaft 18 in a direction of arrow C by a voice coil motor 19 provided on the base 7.
In a disk device like this, at the time of inserting the shaft 9 into the sleeve 10, it is not seldom that foreign matters such as scrap metal powder of burr or wear powder generated at the time of metal processing sometimes enter the sleeve inner space 11. Further, at the time of rotating the sleeve 10, the sleeve 10 sometimes makes contact with the shaft 9 and others, causing the foreign matters to be generated.
These foreign matters 12 are conveyed to the space 11A at the top of the shaft 9 by the airflow which flows from the bottom to the top in the sleeve inner space 11. The foreign matters 12 having been conveyed to the space 11A are carried in the airflow which flows from the bottom to the top of the sleeve inner space 11 and discharged from the air vent 2 into an inner space 13a of a casing, and are driven to be discharged outside by passing through the air vent 2.
The foreign matters 12 thus discharged into the inner space 13a through the air vent 2 adhere to the surface of the disk 14 mounted to the sleeve 10, causing a problem of reduction in functional performance, such as a crush of the head 16 or a recording/reproducing error.
The present invention has an object to prevent the discharge of the foreign matters into the inner space 13a and to improve movement stability and reliability of the disk drive.
A hydro dynamic gas bearing according to claim 1 of the present invention is a hydro dynamic gas bearing, in which a sleeve with one end closed is connected to a front end of a shaft supported at its proximal end to a base on a fixed side, a plurality of hydro dynamic pressure generating grooves are formed on at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve opposite the outer peripheral surface, and the sleeve is supported in a radial direction of the shaft by a pumping action of the hydro dynamic pressure generating grooves, the pumping action being made accompanying rotation of the sleeve, wherein the bearing comprises: a through hole formed to extend from the front end to the proximal end of the shaft and communicating with an outside of the base; and an air vent formed in the through hole and adjusting a pressure between the shaft and sleeve.
According to this configuration, by providing a hollow shaft having an air vent at its top, the rotation of the sleeve increases an air pressure in a sleeve inner space to be higher than an atmospheric air pressure, so that the sleeve is supported at a correct position in the radial direction of the hollow shaft. Fine foreign matters entering between the shaft and the sleeve at the time of assembly of the shaft and the sleeve or foreign matters generated as the sleeve contacts with the shaft and others at the time of rotation of the sleeve are carried in a gas passing through the air vent and guided to the outside of a casing through the through hole of the shaft. Therefore, it is possible to prevent the foreign matters from being discharged into an inner space of the casing and improve reliability of the bearing.
A disk drive according to claim 2 of the present invention is a disk drive comprising a hydro dynamic gas bearing and a casing accommodating therein the bearing, wherein the hydro dynamic gas bearing is configured such that a sleeve with one end closed is connected to a front end of a shaft supported at its proximal end to a base on a fixed side, a plurality of hydro dynamic pressure generating grooves are formed on at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve opposite the outer peripheral surface, and the sleeve is supported in a radial direction of the shaft by a pumping action of the hydro dynamic pressure generating grooves, the pumping action being made accompanying rotation of the sleeve, and wherein the casing, part of which is formed by the base, includes in an inner space thereof: a recording medium mounted to the sleeve; driving mechanisms for rotatably driving the sleeve with respect to the shaft; and a head making access to the recording medium to execute reading and writing of information, the inner space of the casing being communicated with an atmospheric outside through a through hole of the shaft.